This invention relates to improved thermoplastic polyester compositions and a method for producing the compositions. The improved thermoplastic compositions comprise an intimate blend of a glass fiber reinforcing filler with polypivalolactone. The easily processable thermoplastic compositions of the invention have significant property advantages over other reinforced polyester molding resins.
It is well known in the art to improve the physical properties of thermoplastics through glass fiber reinforcement. Strength, stiffness and toughness can be considerably enhanced, and particularly in the case of crystallizable thermoplastics, the resistance to deformation at elevated temperature can be markedly increased. However, when polypivalolactone is reinforced with commercial grades of glass fiber normally used successfully to improve the properties of thermoplastic polyesters, only a minimal increase of strength and toughness is realized. The extent of strength improvement is, in fact, sufficiently small that the polypivalolactone reinforced in the conventional way is not broadly useful for engineering thermoplastic applications.
Polypivalolactone is a thermoplastic polyester having many desirable properties for engineering thermoplastic applications, such as outstanding hydrolytic, thermal and chemical stability, excellent weatherability and relatively high resistance to deformation at elevated temperatures. However, it is somewhat deficient in strength and stiffness for broad usage in engineering thermoplastic applications, where the demanding cases require substantial strength at ambient temperatures and, even more importantly, retention of a considerable degree of strength at elevated temperatures. Since polypivalolactone does exhibit significant advantages over other thermoplastic polyesters, there is a need for a glass reinforced polypivalolactone having acceptable strength properties.